The subject matter discussed in this section should not be assumed to be prior art merely as a result of its mention in this section. Similarly, a problem mentioned in this section or associated with the subject matter provided as background should not be assumed to have been previously recognized in the prior art. The subject matter in this section merely represents different approaches, which in and of themselves may also correspond to implementations of the claimed technology.
Motion-capture systems have been deployed to facilitate numerous forms of contact-free interaction with a computer-driven display device. Simple applications allow a user to designate and manipulate on-screen artifacts using hand gestures, while more sophisticated implementations facilitate participation in immersive virtual environments, e.g., by waving to a character, pointing at an object, or performing an action such as swinging a golf club or baseball bat. The term “motion capture” refers generally to processes that capture movement of a subject in 3D space and translate that movement into, for example, a digital model or other representation.
Most existing motion-capture systems rely on markers or sensors worn by the subject while executing the motion and/or on the strategic placement of numerous cameras in the environment to capture images of the moving subject from different angles. As described in U.S. Ser. No. 13/414,485 (filed on Mar. 7, 2012) and Ser. No. 13/724,357 (filed on Dec. 21, 2012), the entire disclosures of which are hereby incorporated by reference, newer systems utilize compact sensor arrangements to detect, for example, hand gestures with high accuracy but without the need for markers or other worn devices. A sensor may, for example, lie on a flat surface below the user's hands. As the user performs gestures in a natural fashion, the sensor detects the movements and changing configurations of the user's hands, and motion-capture software reconstructs these gestures for display or interpretation.
In some deployments, it may be advantageous to integrate the sensor with the display itself. For example, the sensor may be mounted within the top bezel or edge of a laptop's display, capturing user gestures above or near the keyboard. While desirable, this configuration poses considerable design challenges. As shown in FIG. 11A, the sensor's field of view θ must be angled down in order to cover the space just above the keyboard, while other use situations—e.g., where the user stands above the laptop—require the field of view θ to be angled upward. Large spaces are readily monitored by stand-alone cameras adapted for, e.g., videoconferencing; these can include gimbal mounts that permit multiple-axis rotation, enabling the camera to follow a user as she moves around. Such mounting configurations and the mechanics for controlling them are not practical, however, for the tight form factors of a laptop or flat-panel display.
Nor can wide-angle optics solve the problem of large fields of view because of the limited area of the image sensor; a lens angle of view wide enough to cover a broad region within which activity might occur would require an unrealistically large image sensor—only a small portion of which would be active at any time. For example, the angle φ between the screen and the keyboard depends on the user's preference and ergonomic needs, and may be different each time the laptop is used; and the region within which the user performs gestures—directly over the keyboard or above the laptop altogether—is also subject to change.
Accordingly, there is a need for an optical configuration enabling an image sensor, deployed within a limited volume, to operate over a wide and variable field of view.